Re: [Intel-gfx] [PATCH v2 05/20] drm/i915: Make skl_compute_dbuf_slices() behave consistently for all platforms

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Feb 25, 2020 at 05:30:57PM +0000, Lisovskiy, Stanislav wrote:
> On Tue, 2020-02-25 at 19:11 +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Currently skl_compute_dbuf_slices() returns 0 for any inactive pipe
> > on
> > icl+, but returns BIT(S1) on pre-icl for any pipe (whether it's
> > active or
> > not). Let's make the behaviour consistent and always return 0 for any
> > inactive pipe.
> > 
> > Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_pm.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c
> > b/drivers/gpu/drm/i915/intel_pm.c
> > index a2e78969c0df..640f4c4fd508 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -4408,7 +4408,7 @@ static u8 skl_compute_dbuf_slices(const struct
> > intel_crtc_state *crtc_state,
> >  	 * For anything else just return one slice yet.
> >  	 * Should be extended for other platforms.
> >  	 */
> > -	return BIT(DBUF_S1);
> > +	return active_pipes & BIT(pipe) ? BIT(DBUF_S1) : 0;
> 
> I think the initial idea was this won't be even called if there 
> are no active pipes at all - skl_ddb_get_pipe_allocation_limits would
> bail out immediately. If there were some active pipes - then we will
> have to use slice S1 anyway - because there were simply no other slices
> available. If some pipes were inactive - they are currently skipped by
> !crtc_state->hw.active check - so I would just keep it simple and don't
> call this function for non-active pipes at all.

That's just going to make the caller more messy by forcing it to
check for active_pipes 0 vs. not. Ie. we'd be splitting the
responsibility of computing the dbuf slices for this pipe between
skl_compute_dbuf_slices() and its caller. Not a good idea IMO.

-- 
Ville Syrjälä
Intel
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